Nowcasting

Overview

Nowcasting (aka Nowcast) is turbulence prediction data issued by the SkyPath.

Nowcast data is issued hourly for up to 6 hours forecast.

H3 resolution 5 is used by SkyPath for the nowcast area. Each nowcast item covers ~252.9 square km hexagon area (as per the H3 resolutions table) and 1000 feet of altitude. Each hexagon is connected to the other so this allows for covering the area better. So one nowcast item covers for example FL370..<FL380 or FL380..<FL390.

Setup in DataQuery

By default, the nowcast data fetch is disabled. It should be included in the DataQuery.types list:

SkyPath.shared.dataQuery.types = [.turbulence, .nowcast]

Or using a DataTypeOptions.set(type:enabled:) function :

SkyPath.shared.dataQuery.types.set(type: .nowcast, enabled: true)

It can be enabled or disabled at any time.

When enabled, nowcast will be fetched from the server hourly. Fetched data will be stored on disk and will be available offline.

Nowcast data will be fetched for areas set in DataQuery.polygon and DataQuery.viewport, similar to the turbulence fetch flow.

The SkyPathDelegate.didReceiveNewNowcast() delegate function will be called when the SDK has fetched new nowcast data from the server.

Query

Get nowcast data using a query locally cached on disk data without making a server request.

Use NowcastQuery to get filtered data as a GeoJSON string or as an array of objects.

It blocks the current thread, so using a separate background thread is recommended.

var query = NowcastQuery(
    hours: .now,
    altRange: altRange,
    resultOptions: .geoJSON)
query.polygon = polygon

do {
    let result = try SkyPath.shared.nowcast(with: query).get()
    let geoJSON = result.geoJSON
    // Show geoJSON on the map
} catch {
    print(error)
}

H3 resolution 5 is used by SkyPath for the items area. Each item covers ~252.9 square km hexagon area (as per the H3 resolutions table) and 1000 feet of altitude. Each hexagon is connected to the other so this allows for covering the area better. So one item covers for example FL370..<FL380 or FL380..<FL390.

In order to get items for specific tiles use NowcastQuery.tiles property. It accepts h3 or h3-alt format. Such tile id can be taken from NowcastItem.tile property which is a Tile object with the corresponding properties Tile.key and Tile.keyByCoord or Tile.h3Hex.

GeoJSON vs Items

NowcastQuery.resultOptions determines in which format returns the queried data.

• items will provide an array of NowcastItem objects. It can be used for postprocessing and converting for rendering in a custom way.

• geoJSON will generate a GeoJSON string to visualize on the map. It has a geometry polygon to draw the hexagons and extra properties for each one like severity and others. Please note that the properties fields could not match the NowcastItem fields as it's not equivalent objects.

• geoJSONData is the same as geoJSON just as Data not as String.

note

The GeoJSON string is not intended to provide all the details about each item. It is intended to have minimal details to visualize on the map. NowcastItem can be used to get all details per each item.

Item Details

NowcastItem has all the details about the item.

For example, when need to show item details by tapping on the item on the map, the GeoJSON feature properties could not have all the needed values. Also, it could be hard to find all items in the tapped area using GeoJSON only.

Here is the flow:

1. When tapping the GeoJSON feature on the map, take the h3Hex string from the properties. It's the H3 index of the tapped hexagon.

2. Query data from the SDK in the tapped hexagon.

do {
    let query = NowcastQuery(resultOptions: .items, aggregate: false, tiles: [h3Hex])
    let result = try SkyPath.shared.nowcast(with: query).get()
    // Process `result.items`
} catch {
    print(error)
}

Forecast hour NowcastItem.forecastH means a rounded hour since it was generated, so forecastH=0 will be "now till next rounded hour". For example, if currently it's 14:40 and data was just received the forecastH=0 will be for the range 14:00:00-14:59:59, forecastH=1 for 15:00:00-15:59:59, and so on.

You can use the NowcastHours enum to get exact time ranges from a reference date. However, it's better to use the NowcastItem.ts field, a Unix timestamp for the time this prediction is valid. It takes into account generation time so it will be correct like 15:00:00 or 16:00:00.

At the moment, it's an hourly forecast so each report is valid for an hour since NowcastItem.ts.